KR20130079624A - Methods and systems for providing efficient operation of multiple modes in a wlan system - Google Patents

Abstract

A method and system applies MAC transmission opportunity (TXOP) protection for multiple mode operation in a WLAN system. In particular, MAC mechanisms are defined to support multiple mode CTS frames, and multiple mode CF-End frames sent by the AP, each in a format appropriate for the corresponding mode which also applies to a single mode as a trivial case. MAC mechanisms permit truncation of TXOP duration for releasing the unused portion of the TXOP when no further data for transmission is available. Release of unused protected TXOP is possible for both protected AP transmissions and STA transmissions.

Description

≪ Desc / Clms Page number 1 > METHODS AND SYSTEMS FOR PROVIDING EFFICIENT OPERATION OF MULTIPLE MODES IN A WLAN SYSTEM < RTI ID =

The present invention relates generally to wireless local area networks (WLANs). More particularly, the present invention improves the multi-mode deployment behavior of STAs in the same coverage area.

Currently, various proposals for 802.11n extensions to the 802.11 WLAN standard are being presented and discussed, which will enable higher throughput WLAN devices. These proposals are coming from various wireless consortia including EWC, Joint Proposal and WWiSE. The following describes aspects of these proposals relating to the present invention.

1 shows a Clear to Send (CTS) frame as a MAC control frame defined in the 802.11 standard. The destination address RA of the CTS frame is copied from the source address (TA) field of the immediately preceding request to send (RTS) frame in which the CTS is responding. The duration value is the value obtained from the duration field of the immediately preceding RTS frame minus the time required to transmit the CTS frame and its SIFS (short interframe spacing) interval. If the calculated duration contains fractional microseconds, the value is rounded to the next higher integer.

The CTS frame does not always have to be followed by an RTS frame as described in the 802.11e standard (section 7.2.1.2). The CTS frame may be the first frame in the exchange and may be used to set a Network Allocation Vector (NAV) for MAC level protection for the transmission to be transmitted. When a CTS frame is transmitted as the first frame by the initiating station of the exchange, the CTS can be addressed to itself and is referred to as CTS-to-Self.

Figure 2 shows a Contention Free End (CF-End) frame, which is a MAC control frame that can be transmitted by an AP as a broadcast frame to reset the NAV of all stations in the system and is described in the 802.11 standard. The station receiving the CF-End frame with the base service set ID (BSSID) of the BSS to which the station is associated will reset its NAV value to zero. This resets any existing media protection / reservations. The duration field is set to zero. As shown in FIG. 2, the BSSID is the address of the STA included in the AP. RA is the broadcast group address. FCS is a frame check sequence.

In 802.11n, a proposal has been made to implement extended range support using a different physical layer (PHY) modulation scheme than that used for the Normal Range, which essentially provides two modes of operation . Extended range STAs transmit and receive using space time block code (STBC) PHY modulation, and normal range STAs transmit and receive using non-STBC PHY modulation.

Joint Proposal contribution to 802.11n describes an approach for supporting networks of STAs operating in dual mode where the AP is in two modes of extended coverage and regular coverage. Secondary beacons and dual CTS methods together are used to support extended ranges beyond the regular range. The secondary beacon is transmitted with the secondary beacon bit set to the beacon so that the station knows that the target beacon transmission time (TBTT) for this beacon has an offset. For dual CTS protection, the station initiates a TXOP using the RTS to the AP and the AP responds with first and second CTSs separated by a point control function inter-frame spacing (PIFS). If dual CTS protection is possible, the AP shall protect the STBC TXOP with non-STBC CTS and protect the non-STBC TXOP with STBC CTS. The guard frame will set the NAV for the entire TXOP. The STBC control frame will be used in response to the STBC frame if the dual CTS protection bit is set. Otherwise, a non-STBC control frame will be used. PIFS is used as an interval to separate dual CTSs for non-STBC RTS.

Figure 3 shows a diagram from a WWiSE proposal announcement document for self-managed extended scope protection. Signaling examples for dual mode protection of the normal range (NR) and extended range (ER) stations are shown. The signal sequences 301-305 are associated with EDCA (Enhanced Distributed Coordination Function (DCF) channel access) and the signal sequence 306 is associated with the HCF controlled channel access (HCCA) format. The AP uses the signal sequence (301-302) to protect the TXOP for NR STA and ER STA, respectively. The ER STA protects its TXOP with the signal sequence (303). The signal sequence for 11n NR STA is represented by signal sequence 304 and for legacy NR STA is represented by signal sequence 305. [ In the signal sequence 306, the AP protects the TXOP for the STA using the HCCA format. As shown, the AP sends a CTS in a mode used by the station that transmitted the RTS in response to the RTS from the particular station, or a CTS-to-Self in a mode different from the mode of the station that sent the RTS. Signal.

4 shows a new HT information element according to the WWiSE proposed extension range. The AP signals new HT information elements in the management frame such as beacons, probe responses, etc. to manage the BSS (eg, to support extended range). The new HT information element may also be present in all beacon and probe responses sent by the station in IBSS mode. The HT information element includes fields such as secondary beacon, dual STBC / CTS protection, etc. as shown in FIG. According to the Joint Proposal, the length is not fixed, and the size depends on the number of fields included. The fields are in the order shown in FIG. 4 and any new fields will appear at the end of the existing field. Any fields unknown to the STA will be ignored.

According to the Joint Proposal Specification and the EWC Specification, the following are some definitions related to the Power Save Multi-Poll (PSMP) feature. The PSMP is a MAC frame that provides a time schedule to be used by the PSMP transmitter and the PSMP receiver. The time schedule starts immediately after transmission of the PSMP frame. The downlink transmission (DLT) is the time described by the PSMP frame, which is intended to be used for reception of the frame by the PSMP receiver. Uplink transmission (ULT) is the time described by a PSMP frame, which is intended to be used for transmission of the frame by the PSMP receiver.

Figures 5 and 6 show the PSMP information element format according to the EWC MAC specification. FIG. 5 shows a PSMP parameter set format in which the PSMP consists of a type / subtype management action frame and a broadcast address type. The PSMP parameter set is used to describe the DLT and ULT immediately following the PSMP frame. 6 illustrates STA Info information element format details such as traffic (flow) ID, STA ID, DLT offset and duration, ULT offset and duration.

Figure 7 shows a PSMP sequence consisting of a DLT step and a ULT step following this step. A number of TID block ACKs (MTBAs) are used to transmit the block ACK for multiple TID flows.

There is a need to extend dual mode protection to support multiple mode operation. The current art does not provide robustness and media usage is inefficient because it does not provide a mechanism to recover any unused transmission opportunity (TXOP) duration that is protected by dual CTS transmissions. According to the state of the art, when the STA runs out of data to transmit during the protected TXOP, the medium is wasted for the remainder of the TXOP. There is a need to provide MAC signaling to transfer the remaining unused TXOP to the system.

There is also a need for the PSMP sequence to operate in a multiple mode system in a bandwidth efficient manner. The 802.11n specification includes an incentive to allow only ACK / MTBA in ULT and no data for unscheduled PSMP. In addition, there is no guidance for truncation of the TXOP under dual CTS protection for STAs that can not interpret the CF-End frame.

The present invention seeks to improve the multi-mode deployment operation of STAs in the same coverage area.

The first preferred embodiment is a method and system for extending specific (STBC and non-STBC) dual mode operation in a WLAN system with more general multiple mode operation. A second preferred embodiment is a method and system for improving the MAC protection mechanism in a multiple mode operation, in particular in a single case where multiple CF-Ends transmitted by the AP to enable efficient media utilization And is in a format suitable for the corresponding mode) frame sequence. A third preferred embodiment is a method and system for enhancing a PSMP sequence with multiple mode operation.

According to the present invention, a method and system for providing efficient multi-mode operation in a WLAN system can be provided.

Figure 1 shows a CTS frame in accordance with the 802.11 standard.
Figure 2 shows a CF-End frame format according to the 802.11 standard.
Figure 3 shows a signaling diagram for self-management extended range protection according to WWiSE.
4 shows the management frame HT information element format.
5 shows a PSMP parameter set format.
Figure 6 shows the PSMP STA Info information element format.
Figure 7 shows a PSMP sequence consisting of a DLT step and a subsequent ULT step.
Figure 8 illustrates an exemplary wireless LAN operating in multiple modes.
9 shows a primary beacon format and a secondary beacon format including primary and secondary beacon ID fields.
10 shows a management frame HT information element format including primary and secondary beacon IDs.
Figure 11 illustrates frame transmission of an STA using TXOP protection for a particular mode format.
12 illustrates frame transmission of an AP protecting the TXOP using EDCA.
Figure 13 illustrates frame transmission of an AP protecting the TXOP using HCCA.
Figure 14 shows a frame transmission sequence of an STA releasing an unused TXOP.
15 shows a frame transmission sequence of an AP that distributes an unused TXOP using EDCA.
16 shows a frame transmission sequence of an STA that distributes an unused TXOP using HCCA.
Figure 17 shows a multiple mode PSMP frame sequence.

A more detailed understanding of the present invention may be had by reference to the following detailed description of the preferred embodiments, given by way of example and to be understood in conjunction with the accompanying drawings in which: FIG.

The term "station" or "STA" is used herein to refer to a wireless transmit / receive unit (WTRU), user equipment (UE), mobile station, fixed or mobile subscriber unit, pager, cellular telephone, PDA, But not limited to, other types of user devices. When referred to hereafter, the term "base station" includes but is not limited to a Node B, a site controller, an access point (AP) or any other type of interfacing device capable of operating in a wireless environment.

Hereinafter, for the purpose of describing the present invention, a "mode" is a MAC (Physical Layer) used for communication (transmission and reception) such as a PHY layer, a channel interface, a channel bandwidth (for example, 20 MHz to 40 MHz) It is used to refer to a specific network link under a layer. It should be noted that STAs in different modes may not operate efficiently together in the BSS coverage area unless they are typically controlled and protected by a MAC layer mechanism. The present invention relates to a multiple mode system (e.g., a BSS) in which an STA transmits and receives in multiple modes (more than one mode) in the same coverage area.

FIG. 8 shows an exemplary wireless LAN including an AP, STA1 operating in Mode 1 operation, and STA2 operating in Mode 2 operation. For simplicity, the preferred embodiment is described for two modes of mode 1 and mode 2. However, the present invention can be extended to multiple mode operation involving more than two additional modes.

The following describes three preferred embodiments of the present invention. The first embodiment is a method and system for improving specific (space-time block coding (STBC) and non-STBC) dual mode operation in a WLAN system with more general multiple mode operation. The second embodiment is a method and system for improving the MAC protection mechanism in a multi-mode operation and is particularly applicable to a single mode as a common case, and it is possible to use multiple CF-End Mode) to support the frame sequence. The third embodiment describes a method and system for improving the PSMP sequence with multiple mode operation.

The first embodiment relates to defining a MAC mechanism to support multiple mode operation. Examples of applications for multiple mode operation include (1) a legacy system, (2) a device that supports new modulation settings, (3) a device that may be in a transition mode (new modulation setting) , (4) a mesh network supporting multiple modes, and (5) devices operating on more than one frequency band / channel.

According to a first preferred embodiment, the AP uses two primary MAC mechanisms, namely 1) by sending multicast / broadcast data following beacon / secondary beacons for each supported mode, and 2) By supporting the transmission of multiple CTS frames, each one corresponding to one of the multiple modes supported, multiple mode operation is supported. The challenge for multi-mode protection is that the CTS protection frame must be interpreted as a mode format (modulation, link configuration, etc.) by each of the two communication entities. Thus, if the STA is using a particular mode format, the CTS protection frame must be transmitted and received in that particular format to enable recognition by the STA.

Figure 9 shows a diagram showing a set of preferred frame formats in accordance with the MAC mechanism of the AP. The primary mode frame includes primary beacon 901 followed by multicast / broadcast data 905. The primary beacon includes an HT information element 903. After the defined offset period, secondary mode beacon 902 with HT information element 904 followed by a secondary mode frame containing multicast / broadcast data 906 is transmitted. Referring to FIG. 8, the primary beacon supports STA1 for mode 1 (non-STBC). The secondary beacon supports STA2 using mode 2 (STBC). For purposes of illustration, here Mode 1 and Mode 2 are tailored to primary beacons and secondary beacons, respectively, but alternatively, primary beacons may support Mode 2 and secondary beacons may support Mode 1, depending on system parameters. Returning to our example of the invention, in general, the primary beacon will support all stations using mode 1 and the secondary beacon will support all stations using mode 2. For multiple mode operation, additional secondary beacons will each support each mode used in the system.

During multiple mode operation, the AP transmits beacon / secondary beacon and multicast / broadcast traffic in a format suitable for each mode supported by the system. In a multiple mode system, one of the transmitted beacons (corresponding to various modes) is identified as the primary beacon 901. Each secondary beacon 902 may be transmitted with a time offset (associated with the primary beacon 901 or any other time reference). The time offset can be determined based on system considerations. The time offset may be a configurable system parameter that can be changed dynamically by the AP. The time synchronization function (TSF) time stamp of the secondary beacon 902 may be an actual time stamp. All other fields in the secondary beacon 902 are preferably the same as the corresponding fields in the primary beacon 901. The multicast / broadcast data 906 transmitted after the secondary beacon 902 is preferably the same as the multicast / broadcast data 905 transmitted after the primary beacon 901. Based on the system considerations, each secondary beacon 902 includes extra fields and data that are unique to its mode. Also, based on system considerations, each mode may have extra multicast / broadcast fields and data that is unique to its mode.

Figure 10 shows a preferred format for the HT information element 1000 corresponding to the HT information element 903, 904. HT information element 1000 includes the following fields: element ID 1001, length 1002, control channel ID 1003, extension channel offset 1004, recommended transmission width set 1005, RIFS mode 1006, A control access only 1007, a service interval granularity 1008, an operation mode 1009, a basic STBC MCS 1011, an L-SIG protection allowance 1013, and a basic MCS set 1016. These fields correspond to the proposed management HT information element format shown in FIG. According to the present invention, a multiple mode protection field 1012 and a beacon ID field 1014 are included to support multiple modes. As an example for the dual mode, the beacon ID field 1014 may be one bit, a primary beacon if the HT information element has a value of 0, and a secondary beacon if the value is equal to one. However, in the case of multiple modes, the single bit information element is extended to a size sufficient to identify all existing modes other than the primary mode. As shown in Fig. 10, the beacon ID field 1014 is tagged with bits B9-Bk, where k is selected based on the number of supported modes. For example, in a system using 16 modes, a 4-bit beacon ID field (B9-B12, k = 12) is selected.

FIG. 11 shows an example signaling diagram 1100 for a multi-mode system operating in mode 2 and using n modes including an STA STA2 and an AP protecting a TXOP. An indication that multiple mode TXOP protection is supported by the system is provided by the AP. A preferred mechanism for this indication is for the AP to signal multiple CTS protection fields / bits in the new HT information element multiple mode protection 1012, as shown in FIG. When a multiple CTS protection field / bit is set by the AP and received by the station STA2, the TXOP is initiated by the station STA2 by sending a mode 2 transmit request (RTS) frame 1101 to the AP. The response from the AP is to transmit a number of CTS and CTS-to-Self frames 1102-1105 in a format corresponding to the mode, e.g. modulation, link configuration, etc., so that the TXOP is transmitted to a mode 2 station It can be informed to the station operating in the other mode that it is reserved / protected.

As shown in FIG. 11, the AP transmits the CTS frame 1102 in the mode being used for the TXOP protected by the STA. Here, the STA is the station STA2 that starts the TXOP and operates in the mode 2, and the position of the mode 2 CTS frame 1102 in the multiple CTS frame responses from the AP is first. Alternatively, the location of the CTS frame in this mode may be final, or may be determined by the system based on the priority assigned to the mode. The AP also has a number of CTS-to-Self modes n in all modes except for the mode being used for the TXOP protected by the STA, i.e. CTS-to-Self mode 1, CTS- to-Self frames 1103-1105. The relative order of these CTS-to-Self frames may be arbitrary or may be determined based on system and implementation considerations and on the priority assigned to the mode.

Multiple CTS / CTS-to-Self frames 1102-1105 may be separated by other time durations such as Reduced Inter Frame Spacing (RIFS), which is determined based on PIFS, SIFS (as shown) do. When multiple CTS / CTS-to-Self frames 1102-1105 are completely transmitted, mode 2 TXOP 1106 is initiated.

A plurality of CTS / CTS-to-Self frames transmitted by an AP in response to an RTS frame are applied in the following cases. When a BSS with AP communicates in multiple mode operation using multiple CTS signals, the response by each STA consists of a single CTS frame in a format corresponding to that mode of operation. Alternatively, each STA may be capable of responding with multiple CTS frames, which is particularly useful in an independent Basic Service Set (IBSS) (i. E. No AP and all stations are peers) or mesh scenarios . In this case, the selected STA plays the role of the AP by transmitting a plurality of CTS frames. Otherwise, it may be difficult to tune the CTS response from multiple stations.

FIG. 12 shows an exemplary signaling diagram 1200 of an AP protecting the mode 2 TXOP using EDCA, which corresponds to the dual protection signal sequence 301 of FIG. Here, the AP starts a mode 2 TXOP for itself and starts with a plurality of CTS-to-Self frames 1201-1203 of all modes except mode 2. Again, as in FIG. 11, the sequence of multiple mode CTS-to-Self frames may be arbitrary, or may be determined based on system and implementation considerations and based on the priorities assigned to the modes. Next, the AP sends a Mode 2 RTS frame 1204 containing specific STA address information addressed specifically to STA2 in this example. In response, if the AP has sent data in mode 2, STA2 sends a mode 2 CTS frame 1205, which allows the mode 2 TXOP frame 1206 from the AP to start.

FIG. 13 shows an exemplary signaling diagram 1300 of an AP that protects TXOPs for Mode 2 STA using HCCA, which corresponds to the dual protection signal sequence 306 of FIG. If a plurality of CTS protection fields / bits 1012 are set and transmitted by the AP, the AP will format in a format corresponding to the mode except for the mode being used for the TXOP being protected by the AP in this example mode 2, A plurality of CTS-to-Self frames 1307 to 1310 are transmitted through modulation, link configuration, and the like, and the TXOP is protected in a predetermined mode. The order of the multiple CTS-to-Self frames 1307-1310 corresponding to the multiple modes may be arbitrary or may be determined based on system and implementation considerations and based on the priorities assigned to the modes. A number of CTS-to-Self frames 1307-1310 may be separated by other time durations, such as RIFS, which are determined based on SIFS (as shown), PIFS, or other system factors.

As shown in FIG. 13, following a number of CTS-to-Self frames 1307-1310, other time durations, such as RIFS, determined based on SIFS, PIFS, or other system factors, The CF-poll frame 1311 is transmitted in the mode being used for the TXOP. Here, TXOP 1312 is for mode 2, and thus CF-Poll frame 1311 is mode 2.

According to this multi-mode TXOP protection embodiment, if the TXOP for the STA is protected, the STA must wait until a number of CTS or CTS-to-Self frames are transmitted from the AP before starting its transmission. To achieve this, the following preferred procedures are followed individually or in various combinations. Preferably, the time required to transmit multiple CTS / CTS-to-Self frames by the AP will be known to the STAs in the system. An example of one possible approach is to include this information in the fields of the new HT information element 1000 transmitted by the AP. Alternatively, the station will not start transmission before receiving a CTS response to its RTS, and an explicit time need not be communicated in advance if this CTS response comes last. Another approach is to rely on carrier detection before transmission, i. E. Even after receiving the CTS, the STA will have to wait if the medium is still occupied by a CTS frame in a different mode.

Alternatively, if all STAs are capable of transmitting and receiving in a single common mode format, the common mode format is preferably used to transmit a protection control frame such as RTS and CTS even if they normally communicate in a certain mode. The modulation used to transmit the control frame is typically a basic rate in a certain mode. In each mode, higher speeds are used for data transmission. It can be assumed that the STA supports basic speeds in all modes and supports higher speeds in only one desired / specific mode. In this case, a single RTS frame and a single CTS frame being exchanged between two communication devices in its common format are sufficient to establish protection in a multi-mode system operation.

In all of the above protection mechanisms for multiple mode operation, the protection frame used (i.e., RTS, CTS) preferably sets the NAV for the entire TXOP being protected.

A second preferred embodiment of the present invention provides a MAC mechanism to support efficient use of media in multi-mode operation by releasing unused portions of protected TXOP. Figures 14-16 illustrate exemplary signal sequences of how a number of CF-End frame transmissions may be used to distribute unused TXOPs to improve media usage efficiency.

14 shows an example of an STA that distributes an unused TXOP in mode 2; 11, the STA2 transmits a mode 2 RTS 1401, the AP responds with a plurality of CTS / CTS-to-Self frames 1402-1405, and the TXOP of STA2 corresponds to mode 2 Lt; / RTI > However, in this example, STA2 recognizes that there is no more data available for transmission before the end of TXOP frame 1406. [ STA2 then sends a single End of Data frame 1416, which may be in the format of a CF-End frame. The AP responds with multiple CF-End frames 1407-1409 in all modes. When all CF-end frames are transmitted, an unused portion of the TXOP frame 1406 is distributed to the medium, a new TXOP protection process can be started, and is initiated by another station or AP for its own transmission over the medium .

FIG. 15 shows an exemplary signal sequence of an AP that distributes unused TXOPs during EDCA in mode 2 as an extension of the signal sequence shown in FIG. The AP sends a mode 2 RTS frame 1524 to request a mode 2 TXOP protection, following the multiple mode CTS-to-Self frames 1521-1523. STA2 responds with a mode 2 CTS frame 1525 and clears the manner in which the AP starts its TXOP frame 1506 in mode 2. During the TXOP frame 1506, the AP recognizes that there is no more data to transmit, and accordingly transmits a data end frame 1526, which may be in the format of a CF-End frame. The AP then sends a number of CF-End frames 1527-1529 in all modes to notify all STAs that the AP has completed its mode 2 transmission in the current TXOP frame 1506. [ The TXOP frame 1506 is then truncated and then the unused remainder of the TXOP frame 1506 is distributed for access to another STA or AP in a different mode. The protection of the deployed TXOP follows the multiple mode procedure described above.

16 illustrates an exemplary signal sequence of an STA that distributes an unused TXOP in HCCA in mode 2 as an extension of the signal sequence shown in FIG. The AP transmits a plurality of CTS-to-Self frames 1601-1604 in all modes except the mode of TXOP protection, which is mode 2 in this example. A mode 2 CF-Poll frame 1605 is transmitted, and a mode 2 TXOP frame 1606 for STA2 is started. During the TXOP frame 1606, the STA2 recognizes that its transmission data is exhausted and transmits the data end frame 1612 accordingly. The AP notifies other STAs in all modes using multiple CF-End frames of each mode. The rest of the TXOP is then distributed.

As shown in FIGS. 14 to 16, the AP sequentially transmits a plurality of CF-End frames in the MAC protocol data unit (MPDU) in a transmission format (modulation, link configuration, etc.) corresponding to the mode supported by the AP . A time gap of SIFS (or other time duration determined based on other system factors) is included between CF-End frames.

The following is a further example of a conditional case (individually or in combination) in which this embodiment of distributing a protected TXOP is applicable:

a. After receiving an End-of-Data MAC signal (or a QoS-NULL frame with an ACK response from the AP, for example) from the STA that initiated the TXOP, as shown in FIG. 14;

b. After the AP does not have any data to send and receives a data-terminated MAC signal (or a QoS-NULL frame with an ACK response from the AP, for example) from the STA that initiated the TXOP;

c. The station that initiated the TXOP just stopped sending data;

d. The station that initiated the TXOP just stops sending data and the AP detects it by some means (e.g., carrier sense) and the AP has no data to send;

e. After any media recovery procedure; That is, the AP is able to recover the medium and transmit the CF-End frame so that the station can access the medium;

f. If the AP initiates the TXOP and is done in the downlink transmission and does not expect any uplink transmission;

g. If the AP initiates a TXOP with EDCA and is done in the downlink transmission and does not expect any further uplink transmissions (e.g., a data end signal (as shown in FIG. 15), or an ACK response from the AP Using a QoS-NULL frame having

h. The AP initiates a TXOP with HCCA using CF-Poll and is done in the downlink transmission and does not expect any uplink transmission;

i. The AP initiates the TXOP with the HCCA using the CF-Poll and receives a data termination MAC signal (e.g., a QoS-NULL frame with an ACK response from the AP) from the STA as shown in FIG. 16, When done by link transmission.

The multiple CF-End frames transmitted by the AP preferably comply with the following rules individually or in combination:

a. Multiple CF-End frames will only be transmitted if the current TXOP can be transmitted before it expires. This will be determined by the AP by estimating the remainder of the TXOP and comparing it with the time required to transmit all CF-End frames;

b. If all of the multiple CF-End frames can not be transmitted before the current TXOP expires, the current TXOP will be transmitted as much as possible before it expires;

c. In some cases or system conditions, some or all of the multiple CF-End frames may still be transmitted, even though some or all of them may have to be sent out of the TXOP, even though the current TXOP may not be transmitted before expiration.

The multiple CF-End frames sent by the AP allow all other devices in the system to update their NAV and avoid potential waste or inefficiency in media usage. Multiple CF-End frames from the AP are separated by other time durations, such as RIFS, which are determined based on SIFS or other system factors. The mechanism and order of transmission of multiple CF-End frames (including dual CF-End frames, in the case of dual-mode systems) sent by the AP to distribute unused TXOPs can be made according to the desired option as follows:

a. A plurality of CF-End frames may be transmitted in order of priority determined by a system configuration that may change dynamically, and the priority corresponds to being assigned to a mode supported by the system;

b. The first CF-End corresponds to the mode of the current TXOP and the remainder of the CF-End frame corresponds to the other mode;

c. The order of the plurality of CF-End frames corresponding to the modes supported in the system may be arbitrary;

d. Only one CF-End frame of the format corresponding to the mode of the current TXOP is transmitted if the medium is opened for all stations operating in that mode until the protection for the mode of the current TXOP expires, Gives preference to stations operating in mode;

e. If all the stations can transmit and receive a single common mode format, they will send one single CF-End frame sufficient to update the NAV of all stations in all modes, even if they normally communicate in a certain mode, Mode format should be used.

The following example is described with respect to a dual-mode system application, wherein a dual CF-End frame is within ER (extended range) / NR (regular range) functionality, one CF-End frame is transmitted via ER (STBC modulation) The CF-End frame is transmitted in NR (non-STBC modulation). The following describes one possible implementation of this dual CF-End frame example. STBC and non-STBC CTS frames sent by the AP, typically shown on a beacon if dual CTS protection is possible (i.e., dual CTS protection in the system is possible), and the frame to be transmitted by the STA after the STA acquires the TXOP The STA will terminate the transmission by sending one of the following frames if the remaining TXOPs will allow it (i.e., there is a sufficiently usable TXOP duration remaining after the CF-End frame for distribution) Quot; End of data "or" Truncation of its TXOP ".

Case 1: The CF-End frame according to the modulation scheme (STBC or non-STBC) used by the STA.

Case 2: A QoS-null frame according to the modulation scheme (STBC or non-STBC) used by the STA.

Case 3: Any other type of MAC frame indicating a "transmit end" or "end of data" signal that essentially indicates that the STA no longer has a frame to transmit.

With any one of the display frames (case 1 to case 3), the STA explicitly indicates completion or truncation of its TXOP. If the transmitted frame is a CF-End frame (case 1), it will be interpreted as a NAV reset by another STA capable of receiving the CF-End frame.

Upon receiving any one of the above-mentioned frames (case 1 to case 3) from an STA with a matching BSSID, the AP may request the SIFS duration (or other time duration such as RIFS, which is determined based on other system factors) It will respond with a dual CF-End frame (one STBC CF-End frame and one non-STBC CF-End frame). As another possibility, in case 2 and any other frame that expects an ACK, the AP may first respond with an ACK before transmitting a dual CTS frame. The dual CF-End frame eliminates the inequity towards the STA that is not in the same mode as the STA that owns the truncated TXOP.

If the TXOP is owned by the AP and the system is capable of dual CTS protection (typically indicated on the beacon, ie both STBC and non-STBC STAs are present in the system), the AP will continue to transmit the remaining TXOP If the duration allows this, you can send a dual CF-End frame.

Also, if dual CTS protection is possible in the system (i. E., Both STBC and non-STBC STA are present in the system), as generally indicated in the beacon, the AP will issue a dual CF-End frame An STBC CF End frame and a non-STBC CF-End frame). STAs capable of both modes can transmit a dual CF-End frame if the remaining TXOP duration will allow it, if they want to cut their TXOP.

The spacing between the dual CF-End frames sent by the AP may be other time durations such as RIFS determined based on SIFS, or other system factors. The order of the frames in the dual CF-End frame may be arbitrary, or one of them may be selected to be transmitted first. In a first preferred embodiment, the first CF-End frame will use the same modulation as used for transmission in the TXOP being truncated and the second CF-End frame will use the other modulation. That is, the first CF-End in the STBC TXOP mode is the STBC mode and the first CF-End in the non-STBC TXOP mode is the non-STBC mode.

Note that the above solution has the advantage of both increasing media utilization efficiency and eliminating inequity towards STAs not in modes such as owning a truncated TXOP. This means that until the CF-End transmitted by the owner of the TXOP to truncate the TXOP can not be interpreted by the STA in another mode and thus the AP sends a dual CF-End (or, in general, multiple CF-Ends) This is because you will not be able to access the media. The solution also generally applies to systems with multiple modes (more than two modes).

The following describes a specific embodiment according to the above cases 1 to 3 which specifically applies to the 802.11n standard specification. If dual CTS protection is enabled and the STA acquires the TXOP, and the STA is out of frames, then the STA will indicate the truncation of its TXOP by sending a CF-End frame if the remaining TXOP duration will allow it . For example, this condition may be satisfied if the next decision, i.e., the remaining duration of the TXOP is a CF-End frame duration, an STBC CF-End frame duration, a non-STBC CF-End frame at a known basic rate, Period is greater than the sum of the periods. With CF-End frame transmission, the STA explicitly indicates completion or truncation of its TXOP. The transmission of the CF-End frame will be interpreted as a NAV reset by another STA capable of receiving it. Upon receiving a CF-End frame from an STA with a matching BSSID, the AP will respond with a dual CF-End frame (one for the STBC CF-End frame and one for the non-STBC CF-End frame) after the SIFS duration. If the TXOP is owned by the AP and the system is capable of dual CTS protection, the AP can send a dual CF-End frame if the remaining TXOP duration will allow it if the frame to transmit is exhausted. The spacing between the dual CF-End frames sent by the AP will be SIFS. The first CF-End frame will use the same modulation as that used for transmission in the truncated TXOP, and the second CF-End frame will use the other modulation. That is, the first CF-End in the STBC TXOP mode is the STBC mode and the first CF-End in the non-STBC TXOP mode is the non-STBC mode.

The following describes a simple alternative solution or mechanism that does not need to transmit dual CF-Ends but is less efficient for media use. If the STA or AP uses the Long NAV mechanism to acquire the TXOP and protect the TXOP duration, if there are no more frames to be transmitted, the CF-End frame is transmitted and indicates the truncation or completion of the TXOP. The simple solution of the present invention is essentially to allow the transmission of the CF-End frame by the owner of the TXOP if the system is capable of dual CTS protection (preferably indicated on the beacon) Change. Thus, under these conditions, the TXOP will not be truncated by the owner even if it does not have a frame to transmit anymore. This also applies in the case of systems which generally have several modes (more than two modes).

When the STA receives the CF-End frame (or MPDU) according to the modulation scheme corresponding to its mode, it can update its NAV as follows (for example, reset its NAV to 0):

a. The station updates its NAV after verifying that the BSSID corresponds to its BSS (i.e., the BSS controlled by the AP to which the STA is associated). If the BSSIDs do not match, the STA does not update its NAV.

b. In some cases or implementations, the STA updates its NAV regardless of the BSSID in the CF-End frame.

A third preferred embodiment of the present invention defines a multiple mode PSMP sequence for a multiple mode system. The prior art PSMP sequences are designed to operate for a single mode. So, in order to apply the prior art PSMP sequence to a multiple mode system, each mode will start with a dual CTS-to-Self frame followed by a PSMP frame and a scheduled downlink and uplink transmission. This procedure will have to be repeated for each mode using the prior art PSMP sequence. This is not efficient use of media and is inflexible because multiple mode allocation can not be done with a single PSMP sequence.

Figure 17 illustrates an example of a multiple mode PSMP sequence in accordance with the present invention. Here, the multiple mode PSMP sequence is defined to include a multiple mode CTS-to-Self frame followed by a multiple mode PSMP frame followed by a multiple mode downlink and uplink transmission. A multiple mode PSMP frame defines a schedule for multiple mode downlink and uplink transmissions during a multiple mode PSMP sequence duration. Multiple mode PSMP frames can define the downlink time (DLT) allocation and uplink time (ULT) allocation of a station in various modes in any order determined suitably for application and device performance, and are completely flexible. Examples of assignment ordering include, but are not limited to:

(1) All downlink allocations of the same mode may be lumped together, for example, there may be multiple STAs receiving in the same mode and there may be one STA in each DLT;

(2) all uplink allocations of the same mode can be bundled together;

(3) all uplink allocations are made after all downlink allocations (FIG. 17);

(4) The order of the STAs in the downlink allocation can be maintained in the uplink allocation (FIG. 17).

Many different variations are possible as to how a multiple mode PSMP frame can define downlink time (DLT) allocation and uplink time (ULT) allocation. For example, DLT may be followed by an ULT of the same mode. That is, according to this third preferred embodiment, highly flexible ordering of ULT / DLT in any mode suitable for application and device performance is possible.

Multiple mode PSMP frames may be separated by other time durations such as RIFS determined based on PIFS or other system factors.

The present invention may be implemented as a network having an access point with a plurality of STAs or WTRUs in an application specific integrated circuit (ASIC), digital signal processor (DSP) or software, data link layer, medium access control, and network layer. The present invention relates to an 802.11 based WLAN system or OFDM / MIMO using Radio Resource Management (RRM) and Radio Resource Controller (RRC).

Although the features and elements of the present invention have been described in the preferred embodiments in particular combinations, it is to be understood that each feature or element may be used alone, without the other features and elements of the preferred embodiment, May be used in various combinations together or without other features or elements of the invention. The methods provided herein may be implemented as a computer program, software, or firmware that is implemented in a general purpose computer or a computer-readable storage medium for execution by a processor. Examples of computer-readable storage media include read-only memory (ROM), random access memory (RAM), registers, cache memories, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto- Optical disks, such as ROM disks, and digital versatile disks (DVDs).

Suitable processors include, for example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, a controller, a microcontroller, an ASIC, Array circuit, any other type of integrated circuit (IC), and / or a state machine.

A processor associated with the software may implement a radio frequency transceiver for use in a station (STA), a wireless transmit / receive unit (WTRU), a user equipment (UE), a terminal, a base station, a radio network controller (RNC) Can be used. The STA may be a digital video camera, a video camera module, a video phone, a speakerphone, a vibrator, a speaker, a microphone, a television transceiver, a handsfree headset, a keyboard, a Bluetooth module, a frequency modulation (FM) , A media player, a video game player module, an Internet browser, and / or any wireless local area network (WLAN) module.

Example

1. A method for multiple mode operation in a wireless network having an access point and at least one station (STA), the mode being defined by a network link of the STA,

Transmitting a beacon by the access point; And

And sending multicast and broadcast data for each mode supported by the network.

2. The method of embodiment 1 further comprising supporting a plurality of transmittable (CTS) frames corresponding to the mode.

3. The method of embodiment 1 or 2, wherein each beacon is transmitted for each mode supported by the system in a format suitable for the respective mode.

4. The method of embodiment 3 wherein one of the transmitted beacons is identified as a primary beacon by a primary beacon field or bit in an HT information element transmitted by the AP and the remaining beacons are identified in each mode Lt; RTI ID = 0.0 > beacon < / RTI >

5. The method of embodiment 3 or 4, wherein the secondary beacon is identified by a secondary beacon field or bit in an HT information element transmitted by the AP.

6. The method of embodiment 5 wherein the secondary beacon is transmitted with a time offset relative to a time reference.

7. The method of embodiment 6 wherein the time reference is associated with the primary beacon.

8. The method of embodiment 6 or 7, wherein the time offset is determined based on system considerations.

9. The method as in any one of embodiments 6-8, wherein the time offset is a configurable system parameter that can be dynamically changed by the AP.

10. The method as in any embodiments 5-9, wherein the field in the secondary beacon is the same as the corresponding field in the primary beacon except for a time stamp field unique to the secondary beacon.

11. The method of embodiment 10 wherein the multicast and broadcast data transmitted after the secondary beacon are identical to the multicast and broadcast data transmitted after the primary beacon.

12. The method as in any embodiments 5-9, wherein the secondary beacon includes a field unique to its mode.

13. The method of any one of the preceding embodiments, wherein the network supports protection for multiple mode operation and multiple mode operation by multiple CTS protection bits transmitted by the AP in an HT information element in a medium access control (MAC) ≪ / RTI >

14. The method of embodiment 13 further comprising initiating a transmission opportunity (TXOP) by the STA in a transmission request (RTS) frame sent to the AP.

15. The method of embodiment 14 further comprising transmitting a response comprising a plurality of CTS frames from the AP.

16. The method of embodiment 15 wherein the CTS frame is in a format corresponding to each mode, including modulation or link configuration.

17. The apparatus of embodiment 15 wherein the CTS frame is transmitted as a first frame by a starting station on a network link and the CTS frame is addressed to the starting station as a CTS-to-Self frame,

Protecting the TXOP by the STA; And

Further comprising: transmitting a CTS-to-Self frame in all modes except for the mode being used for the TXOP protected by the STA.

18. The method of embodiment 17 wherein the AP sends each CTS-to-Self frame in each mode format.

19. The method of embodiment 18 wherein the relative order of the CTS-to-Self frames is arbitrary.

20. The method of embodiment 17 wherein the AP transmits each CTS-to-Self frame and the relative order of the CTS-to-Self frames is based on system and implementation considerations, ≪ / RTI >

21. A method for multi-mode operation in an IBSS wireless network having a plurality of STAs operating in multiple modes defined by a link of the STA,

Transmitting a CTS-to-Self frame for each mode of operation such that the first STA represents protection of one mode of TXOP for the first STA or one other STA; And

Transmitting an End-of-Data frame by the STA with the protected TXOP if there is no more data to transmit; And

And distributing the remainder of the TXOP for access by any STA.

22. The method of embodiment 21 wherein the location of the CTS frame in a plurality of CTS frame responses from the AP is first or last, or determined by the network.

23. The method of embodiment 22 wherein the location of the CTS frame in a plurality of CTS frame responses from the AP is further based on a priority assigned to the mode.

24. The method as in any one of embodiments 21-23, wherein the plurality of CTS frames are separated by a time duration determined by network factors.

25. The process as in any one of embodiments 14-24,

Transmitting a plurality of CTS responses for the RTS by the access point; And

And protecting the TXOP of the predetermined mode with a plurality of CTS-to-Self frames.

26. The method according to embodiment 13,

Sending a plurality of CTS-to-Self frames addressed to the AP by an AP; And

Further comprising protecting the TXOP by the AP by transmitting the RTS following the plurality of CTS-to-Self frames.

27. The method of embodiment 26 further comprising transmitting a CTS frame by the STA in response to the RTS.

28. The method of embodiment 26 further comprising: transmitting the CTS-to-Self frame in all modes except for the mode being used for the TXOP protected by the AP.

29. The method as in any one of embodiments 25-28, wherein the plurality of CTS-to-Self frames are in arbitrary relative order.

30. The method of embodiment 26 wherein the relative order of the plurality of CTS-to-Self frames is determined based on system and implementation considerations.

31. The method as in any one of embodiments 25-28 or 30, wherein the relative order of the CTS-to-Self frames is determined based on a priority assigned to the mode.

32. The method as in any one of embodiments 26-31, wherein the plurality of CTS-to-Self frames are separated by a time duration determined by network factors.

33. The method according to embodiment 13,

Transmitting a plurality of CTS-to-Self frames addressed to the AP by an AP; And

Further comprising protecting the TXOP by the AP by sending a CF-poll following the plurality of CTS-to-Self frames.

34. The method of embodiment 33 wherein the plurality of CTS-to-Self frames are separated by a time duration determined by network factors.

35. The method of any one of the preceding embodiments, wherein the AP transmits a plurality of CTS frames and the STA waits until the plurality of CTS frames from the AP are transmitted before the STA initiates its transmission How to wait.

36. A method for controlling media usage during a multiple mode operation in a wireless network having an access point (AP) and at least one station (STA)

Comprising the steps of: transmitting a plurality of contention free end (CF-End) frames in a medium access control (MAC) layer by the AP, wherein the CF-End frame includes a transport format corresponding to a mode supported by the AP .

37. The method of embodiment 36 wherein a time gap between a plurality of CF-End frames is used with a duration determined by a network factor.

38. The method as in any one of embodiments 36-38, further comprising distributing an unused TXOP after receiving an End-of-Data MAC signal from an STA initiating the TXOP.

39. The method of embodiment 38 wherein the unused TXOP is distributed after the AP has no data to send and the AP detects carrier TX detection using an unused TXOP.

40. The method as in any of the embodiments 38-39, wherein the unused TXOP is released after the AP restores the medium and transmits the CF-End frame so that the stations can access the medium.

41. The method as in any one of embodiments 38-40, wherein the unused TXOP is released when the AP initiates a TXOP and is performed in a downlink transmission and does not expect any uplink transmission.

42. The method as in any one of embodiments 38-41, wherein the unused TXOP is released when the AP initiates a TXOP with EDCA and is performed in a downlink transmission and does not expect any uplink transmission any more.

43. The method as in any one of embodiments 38-42, wherein the unused TXOP is deployed when the AP initiates a TXOP with HCCA using CF-Poll and is performed in a downlink transmission and does not expect any uplink transmission Way.

44. The method as in any one of embodiments 38-42, wherein the unused TXOP is released when the AP initiates a TXOP with HCCA using CF-Poll and receives a data termination MAC signal from the STA.

45. The method as in any one of embodiments 36-44, wherein the plurality of CF-End frames are transmitted by the AP when the current TXOP can be transmitted before expiration.

46. The method as in any one of embodiments 36-44, wherein the plurality of CF-End frames are transmitted by the AP as much as possible before the current TXOP expires.

47. The method as in any of the embodiments 36-44, wherein the plurality of CF-End frames are transmitted by the AP, wherein all or a portion of the plurality of CF-End frames may be transmitted before the current TXOP expires. If not, all or some of the plurality of CF-End frames are transmitted out of the TXOP.

48. The method as in any of the embodiments 45-47, wherein the transmission order of the plurality of CF-End frames transmitted by the AP to distribute the unused TXOP is an order of priority determined by the network configuration .

49. The method of embodiment 48 wherein the order changes dynamically.

50. The method as in any embodiments 48-49, wherein the priority corresponds to being assigned to a mode supported by the network.

51. The method as in any of the embodiments 48-50, wherein the first CF-End frame corresponds to the current TXOP mode and the remaining CF-End frame corresponds to the priority of the mode.

52. The method of embodiment 51 wherein the order of the plurality of CF-End frames corresponding to the modes supported in the system is arbitrary.

53. The method as in any of the embodiments 48-50, wherein one CF-End frame is selected for the current TXOP so that the medium is open to all stations operating in that mode until protection for the current TXOP expires. Mode. ≪ / RTI >

54. The network as in any of the embodiments 45-47, wherein the network is a dual mode network using an extended range mode and a regular range mode, wherein one CF-End frame is a space time block code (STBC) Modulation scheme, and the other CF-End frame is transmitted in the non-STBC modulation scheme for the normal range mode.

55. The process as in any one of embodiments 36-54,

Receiving the CF-End frame by the STA; And

Further comprising updating its network assignment vector (NAV) in response to the received CF-End frame.

56. The method of embodiment 55 wherein the CF-End frame includes a Basic Service Set ID (BSSID), the STA determines that the BSSID corresponds to its default service set controlled by the AP to which the STA is associated And to update his NAV after verification.

57. The method as in embodiment 55 wherein the CF-End frame comprises a Basic Service Set ID (BSSID) and the STA determines whether the BSSID corresponds to its base service set controlled by the AP to which the STA is associated How to update your NAV, regardless of whether it is.

58. A method of controlling media access during a multiple mode operation in a wireless network using a series of power save multiple poll (PSMP) frames,

Transmitting a multiple mode CTS-to-Self frame;

Transmitting a multiple mode PSMP frame; And

Transmitting a multiple mode downlink and uplink transmission.

[0064] [0064] 59. The method of embodiment 58 wherein the PSMP frame defines a schedule for the multiple mode downlink and uplink transmissions for a multiple mode PSMP sequence duration.

60. The apparatus of embodiment 58 or 59, wherein the PSMP frame defines a downlink time (DLT) assignment and an uplink time (ULT) assignment of the station in various modes in any order suitably determined for the device's capabilities and applications. How to do it.

61. The method as in any embodiments 58-61, wherein the PSMP frames are separated by a time duration determined by network factors.

62. A wireless communication system configured with a MAC mechanism to support protection of TXOPs for a plurality of operating modes,

A plurality of stations (STA) operating in two or more support modes; And

An access point (AP) configured to transmit a plurality of CTS frames, each of which corresponds to a respective mode supported by the system.

63. The system of embodiment 62 wherein the CTS frame is transmitted in response to an RTS frame by the STA.

64. The system of embodiment 62 wherein the STA is configured to indicate end of transmission when there is no data to transmit.

65. The system of embodiment 64 wherein the STA sends a CF-End frame for the indication.

66. The system of embodiment 62, wherein the STA transmits the CF-End frame in a modulation scheme used by the STA.

[0065] [0070] 67. The system of embodiment 62, wherein the STA indicates termination of the transmission by sending a QoS-null frame.

68. The system of embodiment 67 wherein the STA sends the QoS-null frame in a modulation scheme used by the STA.

[0065] [0070] 69. The system of embodiment 62, wherein the STA indicates termination of the transmission by transmitting any type of MAC frame.

[0064] [0070] 70. The system of embodiment 62, wherein the indication of the end of transmission is interpreted by another STA as a network assignment vector (NAV) reset.

71. The system of embodiment 62, wherein the AP transmits a plurality of CF-End frames in all supported modes upon reception of the indication of the end of transmission.

72. The system of embodiment 62 wherein the CF-End frame is separated by a SIFS duration.

73. The system of embodiment 62, wherein the CF-End frame is transmitted in a RIFS duration.

74. The wireless communication system of embodiment 62, wherein the AP transmits an acknowledgment (ACK) before transmitting the CF-End frame.

75. The system of embodiment 62 wherein the AP transmits one STBC CF-End frame and one non-STBC CF-End frame.

Claims (20)

In the method for use in an access point (AP),
Comprising: receiving a request-to-send (RTS) frame from a station (STA) indicating a request for a transmit opportunity (TXOP);
Transmitting an indication of a TXOP in response to the RTS frame, wherein the indication of the TXOP is a clear-to-send (CTS) frame;
Receiving packet data from the station during the TXOP;
(STBC) frame or a first non-STBC CF-End frame (STBC) if the station does not have additional packet data to transmit Receiving an indication of a truncation of the TXOP including the TXOP; And
Transmitting the second STBC CF-End frame and the second non-STBC CF-End frame in response to the indication of the truncation of the TXOP
Gt; access point, < / RTI > 2. The method of claim 1, wherein receiving an indication of a truncation of the TXOP occurs when there is sufficient TXOP duration remaining. 3. The method of claim 2, wherein the remaining TXOP duration is one of a CF-End frame duration, an STBC CF-End frame duration, a non-STBC CF-End frame duration, and two SIFS (short interframe spacing) The remaining TXOP duration is sufficient if the sum is greater than the sum. 2. The method of claim 1, wherein the indication of disconnection of the TXOP represents a network allocation vector (NAV) reset for the access point. 2. The method of claim 1, wherein each of the second STBC CF-End frame and the second non-STBC CF-End frame represents an end of a contention free interval. 2. The method of claim 1, wherein a short interframe spacing (SIFS) duration separates the second STBC CF-End frame and the second non-STBC CF-End frame. 2. The method of claim 1, wherein receiving an indication of disconnection of the TXOP comprises receiving a CF-End frame using the same modulation type as the received packet data. Way. In an access point (AP),
A receiver configured to receive a request-to-send (RTS) frame from a station (STA) indicating a request for a transmit opportunity (TXOP);
A transmitter configured to transmit an indication of a TXOP in response to the RTS frame, wherein the indication of the TXOP is a clear-to-send (CTS) frame;
The receiver also receives packet data from the station during the TXOP and if the station does not have any additional packet data to transmit, the first space-time block code (STBC) -End) frame or a first non-STBC CF-End frame,
Wherein the transmitter is further configured to transmit a second STBC CF-End frame and a second non-STBC CF-End frame. The access point of claim 8, wherein the receiver is further configured to receive an indication of truncation of the TXOP if sufficient TXOP duration remains. 10. The method of claim 9, wherein the remaining TXOP duration is of a CF-End frame duration, STBC CF-End frame duration, non-STBC CF-End frame duration, and two short interframe spacing (SIFS) durations. An access point for which sufficient TXOP duration remains if greater than the sum. 9. The access point of claim 8, wherein the receiver is further configured to receive an indication of truncation of the TXOP using a CF-End frame using the same modulation type as the received packet data. 9. The access point of claim 8, wherein the indication of truncation of the TXOP indicates a network allocation vector (NAV) reset for the access point. The access point of claim 8, wherein each of the second STBC CF-End frame and the second non-STBC CF-End frame represents an end of a contention free interval. The access point of claim 8, wherein the receiver is further configured to receive the first STBC CF-End frame and the first non-STBC CF-End frame separated by a short interframe spacing (SIFS) duration. . A method for use in a station (STA),
Transmitting a request-to-send (RTS) frame representing a request for a transmit opportunity (TXOP) to an access point (AP);
Receiving an indication of a TXOP in response to the RTS frame, wherein the indication of the TXOP is a clear-to-send (CTS) frame;
Transmitting packet data to the access point using a space-time block code (STBC) during the TXOP;
Transmitting an indication of truncation of the TXOP comprising a first STBC CF-End (contention free-end) frame if the station does not have additional packet data to transmit; And
Receiving a second STBC CF-End frame from the access point in response to transmission of a non-STBC CF-End frame and an indication of disconnection of the TXOP
≪ / RTI > 16. The method of claim 15, wherein the short interframe spacing (SIFS) duration separates the second STBC CF-End frame and the non-STBC CF-End frame. 17. The method of claim 16, wherein one of the second STBC CF-End frame and the non-STBC CF-End frame is of the same modulation type as the transmitted packet data. In the station (STA),
A transmitter configured to transmit a request-to-send (RTS) frame indicative of a request for a transmit opportunity (TXOP) to an access point (AP);
A receiver configured to receive an indication of a TXOP in response to the RTS frame, wherein the indication of the TXOP is a clear-to-send (CTS) frame;
The transmitter may also transmit packet data to the access point during the TXOP and may include space-time block code (STBC) CF-End frames and non- And to transmit an indication of truncation of the TXOP including an STBC CF-End frame. 19. The station of claim 18, wherein the transmitter is further configured to transmit the STBC CF-End frame and the non-STBC CF-End frame separated by a short interframe spacing (SIFS) duration. 20. The station of claim 19, wherein the transmitter is further configured to transmit one of the STBC CF-End frame and the non-STBC CF-End frame with the same modulation type as the transmitted packet data.

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